Fort Hood officials have to chase brass pickers off ranges and out of the impact area all the time.
When I was in the Infantry School at Benning in the early 70s, the patrolling exercise was held on leased land south of the post. You could tell where the next ambush spot was because there was always a couple of pickup trucks usually with a whole family, husband, wife, kids sitting under a tree just waiting for the ambush. After the patrols left the area they would move in and police up the brass.
During the exercises held on post, you could navigate to the next objective by looking for the roach coaches.